GRAFTING OF V2O5 MONOLAYERS ONTO TIO2 FROM ALKOXIDE PRECURSORS - A DIFFUSE REFLECTANCE FTIR STUDY

Vanadia layers are immobilized on a titania support by the selective reaction of the surface hydroxyl groups with the reagent vanadyl triisopropoxide. The impregnation and calcination processes are studied in situ by diffuse reflectance FTIR spectroscopy. The isopropoxide groups of the precursor are oxidized to acetone during calcination; this result is confirmed by acetone adsorption and isopropanol oxidation experiments. Calcination in an inert gas atmosphere (argon or nitrogen) generates a reduced state of the catalyst; UV-VIS reflectance spectroscopy shows that vanadium(IV) coexists with vanadium(V) in the first immobilized monolayer, which consists of polymeric arrays of distorted VO6 coordination units. Observation of the overtones of the VO stretching vibration yields valuable information on the coordination geometry, as well as on the oxidation and hydration state. An overtone band observed at 2060 cm- is attributed to VO2+ ions at an oxygen-deficient surface site. © 1990.